|P0128 – Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)|
|Description: Indicates the thermostat monitor has not achieved the required engine operating temperature within a specified amount of time after starting the engine.
Possible Causes: • Insufficient warm up time
• Low engine coolant level
• Leaking or stuck open thermostat
• Damaged engine coolant temperature (ECT) sensor
• Damaged cylinder head temperature (CHT) sensor
Diagnostic Aids: Refer to Section 1, Thermostat Monitor for system information.